1. Technical Field of the Invention
The present invention relates generally to a multi-rotor synchronous machine which may be used as a generator/motor for automotive vehicles such as hybrid vehicles, and more particularly to a compact and reliable structure of a multi-rotor synchronous machine.
2. Background Art
Typical permanent magnet synchronous machines are capable of producing a higher output and have the structure easy to reduce in size as compared with other types of synchronous machines and thus suitable for use as driving motors of hybrid vehicles or electric vehicles. However, increasing a magnet-produced magnetic field in such a driving motor in order to ensure a sufficient torque during rotation of the motor at low speeds causes an excessive armature winding-induced voltage to be applied to semiconductor elements of a driving circuit during rotation at high speeds undesirably. In order to avoid this problem, any means is needed which is designed to reduce the magnetic field produced during rotation of the motor at high speeds.
U.S. Pat. No. 5,955,807 (Japanese Patent First Publication No. 10-304633), issued on Sep. 21, 1999, assigned to the same assignee as that of this application teaches a stationary field coil/magnet synchronous machine which includes permanent magnets installed in a rotor core, magnetically coupling members inserted into the rotor core in an axial direction thereof to short-circuiting the permanent magnets magnetically, a stationary yoke installed inside the rotor core, field coils provided around the rotor core. The synchronous machine works to energize the field coils to regulate the quantity of magnetic flux flowing through the magnetically coupling members to control an effective quantity of magnetic flux interlinking with the armature windings, thereby regulating the voltage generated by the armature windings.
EP 0901923 A2 discloses an automotive rear-mounted motor generator which is disposed between a crankshaft and a transmission and driven by the crankshaft. The user of the rear-mounted motor generator allows auxiliary mechanical parts to be mounted along a belt in front of the engine which also serve to minimize the slippage of the belt on a small-diameter pulley for driving the motor generator.
The synchronous machine, as taught in the former document, has a problem that the structure is complex.
The motor generator, as taught in the latter document, encounters drawbacks in that the mounting of the motor generator between the crankshaft and the transmission installed behind the crankshaft causes the overall length of the power train to be increased, thus resulting in increases in size and weight of an assembly of the power train and its cover and also results in a difficulty in ensuring the rigidity sufficient to resist mechanical vibrations and deformation of the power train.